WeakMap.js

function WeakMap() {
    this.keys = [];
    this.values = [];
}
WeakMap.prototype.set = function set(k, v) {
    // look for existing keys first
    for (var kI = 0; kI < this.keys.length; kI++) {
        if (this.keys[kI] === k) {
            this.values[kI] = v;
            return;
        }
    }

    this.keys.push(k);
    this.values.push(v);
}
WeakMap.prototype.get = function get(k) {
    for (var kI = 0; kI < this.keys.length; kI++) {
        if (this.keys[kI] === k) {
            return this.values[kI];
        }
    }
}
WeakMap.prototype.remove = function remove(k) {
    for (var kI = 0; kI < this.keys.length; kI++) {
        if (this.keys[kI] === k) {
            this.keys = this.keys.splice(kI, 1);
            this.values = this.values.splice(kI, 1);
            return;
        }
    }
}